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My thoughts on my first Class D amp

I recently started 2 threads on this site, Narrowing down choices in a Power Amp  and also High Power Amp, Does it Matter at Lower Volumes.

I am grateful for all the input, and thought I would share the results of those posts.

Summary is: I have a Baetis Audio Server, going into a T+A Dac8, into a Mark Levinson ( ML ) 326S into a ML532H power amp. The amp loses a channel on occasion, with strange popping noises sometimes, other times just a single ( not very loud pop ). Time to get this amp fixed or buy another amp.

Well, I am getting the amp fixed, but I bought a Class D RCVTech set of monoblocks. 

So, having said all this, WOW. Very happy.

My wife and I sat down last night, and played a variety of music, from the Baetis server. No new music, no streaming, existing tunes we have listened to for years. Nothing but an amp swap.

The RCVTech MPA-1200 monoblocks 

1)  definitely better stereo separation, 

2) definitely way better bass, these monoblocks double down to 700 wpc at 4 ohms, something the ML532H did not do. A world of difference on bass

3) overall better sound, even at low volume.  Not bright or fatiguing at any time. 

4) more detail, listening to existing tracks we have owned for years, more small background detail, 

I wasn't fully sure of what I was buying, but, now, I realize that while I will repair the ML532H, its future use is in question. I am keeping these Monoblock RCVTech MPA-1200 amps in place. 

The buying process was easy, the right questions were asked, delivery was fast, for a customized build.

I have the Class A input with 380 wpc at 8 ohms, 700 wpc at 4 ohms, 700 wpc at 2 ohms, THD + N = 0.0009%.

Since this is Class D, not sure how much more money I would have to spend to better this with a conventional build Class A amp?  I was considering Pass Labs, who were suggesting XA100.8 or larger.  Some day I may actually get to hear these Pass Lab amps, but, there is no urgency, now.

 

robeffy
rikkipuu's avatar
rikkipuu
354 posts
 

Some speakers (like 86dB Magnepan's) need high current to shine.  I replaced an vintage entry 50 WPC Levinson amp with a high power 500 WPC class D and it was better sounding but I think that was because the caps on the ML were worn and it could not deliver the current needed.  At high dB's the sound of the Class D got unpleasant, I think because the Maggies were starving for current or the Class D I used wasn't right for my speakers.

I replaced the Class D with a 60 WPC Pass XA60.8 with less than 20% of the rated output of the Class D and night and day difference for the better all around but especially at louder (not loud) levels.  With the Pass the sound swelled as the loudness increased, it's like listening to waves crash on rocks at the beach from 30 yards out and then moving to standing on the rocks.  The Class D did not do this but rather took on a harder honking character as the volume rose.

I found an interesting paper on output filters of Class D amps.  

https://www.eetimes.com/understanding-output-filters-for-class-d-amplifiers/

Apparently the design of the low pass output filter is critical and is referred to as "the heart of a Class D amplifier". Class D amplifiers generally use a low-pass filter to attenuate the switching noise in the output waveform while passing the audio signal to the loudspeaker.

While the paper is above my head in general it does make the statement that the output filter's "Inductance" and "Q value" need to be designed around the impedance of the speaker!  If you change the Impedance (the Speaker) the optimum Inductance and Q value of the filter changes also changes.  It then goes on to describe what to me are compromises to work with a range of impedances.

I suspect that speakers that provide a difficult load will not shine with Class D amplifiers just like Maggie's don't shine without high current amps.  Class D likely sounds best with simple loads centered around the designed output filter's selected optimum speaker impedance.

Of course I am no engineer and I have limited experience with Class D and this is just what makes sense to me.

 

 

limomangus's avatar
limomangus
1,993 posts
 

Interesting answers you guys are giving on class d amps.

curiousjim's avatar
curiousjim
5,925 posts
 

@robeffy 

Always happy to hear happy news and reviews when someone gets some new equipment. Here’s to many many hours of listening!

My wife and I sat down last night, and played a variety of music, from the Baetis server. 

robeffy's avatar
robeffy OP
79 posts
 

@curiousjim Thanks... we are enjoying the tunes.  Today was super busy, got in an hour or so of listening and reading.  My wife is doing an art show on next Saturday, and today she was interviewed for another show.  Oh boy, what started out as a 1 night event 10 years ago has resulted in over 2600 paintings, and around 5-6 events she is involved in at the moment... 

doni
448 posts
 

"I suspect that speakers that provide a difficult load will not shine with Class D amplifiers just like Maggie's don't shine without high current amps.  Class D likely sounds best with simple loads centered around the designed output filter's selected optimum speaker impedance."

I found just the opposite.  My Class D amps seem to sound better when driving 4ohm speakers, as opposed to 8ohm speakers.  Just another data point, not saying one is right and the other is wrong.

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